add contextlib.nullcontext

Author: smurfix

python-stdlib/contextlib/contextlib.py

@@ -173,3 +173,29 @@ def __exit__(self, *exc_details):
         if pending_raise:
             raise exc_details[1]
         return received_exc and suppressed_exc
+
+class nullcontext:
+    """Context manager that does no additional processing.
+
+    Used as a stand-in for a normal context manager, when a particular
+    block of code is only sometimes used with a normal context manager:
+
+    cm = optional_cm if condition else nullcontext()
+    with cm:
+        # Perform operation, using optional_cm if condition is True
+    """
+
+    def __init__(self, enter_result=None):
+        self.enter_result = enter_result
+
+    def __enter__(self):
+        return self.enter_result
+
+    def __exit__(self, *excinfo):
+        pass
+
+    async def __aenter__(self):
+        return self.enter_result
+
+    async def __aexit__(self, *excinfo):
+        pass